Process for fixedly joining grinding wheel rim to grinding wheel core



United States Patent 3,470,047 PROCESS FOR FI DLY JOINING GRINDING WHEEL RIM TO GRINDING WHEEL CORE Chester Griswold Bragaw, Jr., West Chester, Pa., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Dec. 1, 1965, Ser. No. 510,972 int. Cl. 1332b 31/20; 82% 2.7/12 U.S. Cl. 156-83 5 Claims ABSTRACT OF THE DISCLOSURE A process of fixedly jOining an abrasive filled resin bonded grinding wheel rim to a metal grinding wheel core by applying an adhesive which preferably is heat curable to at least one of the rim or core, followed by snugly fitting the rim over the core, and introducing a hoop strain on the rim equal to an expansion of the internal circumference of the rim of from 0.5 to 1.5 percent preferably by allowing a precooled core and a preheated rim to come to thermal equilibrium.

This invention relates to a process for fixedly joining a grinding Wheel rim to a grinding wheel core, and more particularly, to a process for fixedly joining an abrasive filled, resin-bonded, grinding wheel rim to a metallic core.

Because of the high cost of certain excellent abrasive materials, such as particulate diamonds, it is the practice when making grinding wheels to manufacture them in a form which consists of an internal metallic core in the form of a disk surrounded by a continuous rim or band of an abrasive filled, resin-bonded material which is uniformly disposed around the periphery of the core. In early wheels the peripheral rim was formed in situ around the core by the application of heat and pressure to the particulate abrasive-resin mixture. Later technology led to performing a continuous rim or band of the abrasiveresin mixture, tightly fitting this preformed rim around the core and then free-sintering the rim-core assembly.

The heretofore produced grinding wheels have suffered from the disadvantage that, under wear, the rim has tended to separate from the core. This has resulted from the combination of several factors such as differing coefiicients of expansion of the rim and core, centrifugal force and the torque couple developed when the grinding surface comes into contact with the workpiece.

In accordance with the present invention there has been discoverd a new process for the joining of the grinding wheel rim to the core so that the rim will be fixedly joined to the core and will not separate therefrom under normal operating conditions.

It has been discovered in accordance with the present invention that a unique combination of chemical and mechanical treatments are necessary to insure that an abrasive filled grinding wheel rim will be fixedly joined to a grinding wheel core.

In accordance with the present invention it has been discovered that a chemical adhesive will bind the grinding Wheel rim to the grinding Wheel core and prevent lateral disengagement and that a relatively uniform hoop strain introduced in the grinding wheel rim will prevent radial disengagement of the rim from the core. It will be appreciated by those skilled in the art that it is necessary to prevent both lateral and radial disengagement of the rim from the core.

In order to prevent lateral disengagement a chemical adhesive is applied to at least one of the surfaces to be joined. The surface of the metallic core must be in such condition that it is suitable to maintain an adhesive bond. It must be free of foreign, non-adherent material and ice preferably will have a roughened surface. The roughened surface can be obtained by chemical etching, shallow knurling, sand blasting, and the like.

It has been found preferable to employ a heat-curable, temperature-resistant adhesive in securing grinding wheel rims to grinding wheel cores when the grinding wheels are to be subjected to uses which will produce high internal wheel temperatures due to high friction because such high temperatures will tend to weaken the adhesive bond formed by adhesives which are not resistant to high temperatures.

In addition to the lateral bond obtained by the aforementioned adhesive, it is necessary to obtain a radial bond. In accordance with the present invention this can be achieved by introducing a relatively uniform hoop strain in the rim when the rim is snugly fitted over the core. This strain will provide a compressive stress by the rim upon the core and will serve to prevent radial disengagement and fracture of the glue-line.

It will be understood by those skilled in the art that the strain introduced in the rim need not be absolutely uniform but must be relatively uniform or a portion of the grinding wheel rim will be subject to fracture thus eliminating the required hoop strain throughout the rim. It will be appreciated by those skilled in the art that a resin-bonded grinding wheel rim will possess suflicient elasticity to develop a relatively uniform hoop strain therein when a relatively uniform radial force is applied thereto.

The relatively uniform hoop strain can be introduced in the grinding wheel rim by shrinking thereupon a heat expanded, abrasive filled rim. When the rim-core assembly is allowed to come to thermal equilibrium, the shrinkage of the rim about the core will introduce a hoop strain into the rim. In addition, the core can be precooled prior to the fitting of the rim so that a greater expansion-com traction differential Will be achieved upon the assembly reaching thermal equilibrium, thereby introducing a larger hoop strain into the grinding wheel rim.

Alternatively, the requisite hoop strain can be introduced in the grinding wheel rim after it is snugly joined about the core by expanding the core. The core can be expanded radially Within the rim by applying pressure to the side surfaces thereof. It will be obvious to those skilled in the art that such radial expansion of an internal member will result in the introduction of a hoop strain in a relatively elastic, resin-bonded grinding wheel rim snugly fitted circumferentially thereabout.

It has been determined in accordance with the present invention that in order to achieve a suitable radial bond between the grinding wheel rim and core a relatively uniform hoop strain must be introduced in the grinding wheel rim. While this strain will vary, depending on the size of the Wheel involved, it has been discovered that this strain must be equal to that which is caused by the expansion of the internal circumferential surface of the grinding wheel rim of from 0.5 to 1.5 percent. Expansion of less than 0.5 percent will not produce a satisfactory bond. Expansion in excess of 1.5 percent will, on the other hand, result in fracturing the grinding wheel rim.

I claim:

1. A process for fixedly joining the interior circumferential surface of an abrasive filled, resin-bonded grinding wheel rim to the exterior circumferential surface of a metallic grinding wheel core which includes the steps of:

(1) applying to at least one of the surfaces to be joined an adhesive,

(2) snugly fitting said rim over said core, and

(3) permanently introducing a relatively uniform hoop strain in said rim equal to that caused by the expan- 3 4 sion of 0.5 to 1.5 percent of said internal circum- 5. The process of claim 4 including the step of precociferential surface of said rim. ing said core below room temperature.

2. The process of claim 1 in which said adhesive is a heat-curable, temperature-resistant adhesive and including References Cited the step of: 5 UNITED STATES PATENTS a i g said adhesive 2,121,746 6/1938 Sanford 51-278 3. The process of claim 1 in which said relatively 2,348,696 5/1944 Schabacker 29-84 form hoop strain is introduced by the pressure expan ion 2,467,596 4/1949 Pratt 51-309 XR of said core. 2,498,357 2/ 1950 Breisch 29148.2

4. The process of claim 1 in which said relatively uni- 10 form hoop strain is introduced by thermally expanding EARL BERGERT: Primary Examiner said grinding wheel rim prior to the step of snugly fitting M. E. McCAMISH, Assistant Examiner said rim over said core and then allowing said rim and said core to come to thermal equilibrium, thereby shrink- 15 U3 CL ing said rim about said core. 51309; 15685, 293 

